Communications System, Apparatus and Method

ABSTRACT

A communications signal repeater apparatus ( 106, 110, 114, 118 ) is disclosed which is configured to receive a communications signal from a cable network  105.  The communications apparatus is further configured to delay the communications signal by a delay period relative to a delay parameter and configure the delayed communications signal for transmission over a radio communications channel. The delayed communications signal is converted to a radio signal and output to antenna ( 108, 112, 116, 120 ) for transmission over the air. A communications system incorporating communications apparatus is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of United Kingdom Application No.GB1110292.8, filed Jun. 17, 2011; U.S. Provisional Application No.61/502,825, filed Jun. 29, 2011; United Kingdom Application No.GB1119764.7, filed Nov. 16, 2011; U.S. Provisional Application No.61/568,088, filed Dec. 7, 2011, all of which are incorporated byreference in their entirety. In addition, this application is related toU.S. patent application Ser. No. ______ (attorney docket 28793-20954),titled “Communication System, Apparatus, and Method” with inventor EurosDavies, filed Jun. 13, 2012, and U.S. patent application Ser. No. ______(attorney docket 28793-20955), titled “Communication System, Apparatus,and Method” with inventor Euros Davies, filed Jun. 13, 2012.

BACKGROUND

1. Field of Art

The present disclosure relates to communications systems, apparatus andmethods therefore. In particular, but not exclusively, the presentdisclosure relates to private mobile radio (PMR) communications systemssuch as, without limitation, the Terrestrial Trunked Radio (TETRA)system and the P25 or APCO-25 Land Mobile Radio system.

2. Description of the Related Art

PMR communications systems, and TETRA in particular, are suitable foruse by emergency services, government agencies, public safety networksand the military where security and reliability of communications is ofparamount importance. PMR systems are also used in commercialenterprises, for example in distributed or wide area locations such aslarge industrial sites, mine environments and the like.

A PMR system often comprises a single main site over which radiocommunications signals are transmitted from a Base Transceiver Station(BTS). Such a site may be termed a “cell” or “main site”. Mobiletransceiver units, termed “Mobile Stations (MS)” in the TETRA standardlexicon, receive and transmit radio communications from and to the BTSwhen in the site/cell coverage area. In common with many radiocommunication systems, PMR radio systems such as TETRA can suffer fromgaps in coverage due to the terrain, intervening structures such asbuildings and within buildings or tunnels for example. To overcome thepoor signal conditions repeater stations known as Trunked Mode Operation(TMO) repeaters are used to extend coverage into the affected area tofill gaps in the outdoor coverage or to extend coverage into buildingsand tunnels. Without limitation to a particular system or communicationsprotocol, WCDMA systems may also require repeaters to extend coverageinto buildings, tunnels or the like and to mitigate obstruction causedby terrain features.

Poor signal conditions are a particular problem in urban areas andwithin buildings and tunnels since radio propagation is obstructed bythe building materials such as bricks and concrete and also earthformations when seeking to propagate radio into tunnels. In suchenvironments, the radio signal is propagated by a cable or fiber to arepeater station which re-transmits the radio signal over its localenvironment within the building or tunnel for example.

Aspects and embodiments of the present disclosure were devised with theforegoing in mind.

SUMMARY

Viewed from a first aspect the present disclosure provides acommunications signal repeater apparatus, configured to receive acommunications signal from a cable; delay the communications signal by adelay period relative to a delay parameter; and configure a delayedcommunications signal for transmission over a radio communicationschannel.

Viewed from a second aspect the present invention provides acommunications system, comprising: a cable network for distributing acommunications signal; a communications signal distribution moduleoperative to receive a communications signal for distribution over thecable network and configurable to couple to the cable network; and firstand second repeater communications apparatus as set out aboverespectively coupled to the cable network for receiving thecommunications signal from the distribution module.

Viewed from a third aspect the present invention provides a method ofsynchronizing signals transmitted from two or more repeatercommunications apparatus coupled to receive a communications signalsdistributed over a cable network, the method comprising: introducing afirst delay in the communications signal relative to a delay parameterin a first communications apparatus; introducing a second delay in thecommunications signal relative to the delay parameter in a secondcommunications apparatus; wherein the first and second delay areconfigured to delay the communications signal at the first and secondcommunications apparatus such that they are synchronized to within adelay spread parameter for the cable network.

Embodiments in accordance with the first, second and third aspectsprovide for the synchronization of signals distributed over a cablenetwork. The delay parameter may be selected to ensure that the radiosignals transmitted from each repeater apparatus are synchronizedthereby reducing the likelihood of a mobile terminal operative toreceive the radio signals experiencing unacceptable inter-symbolinterference.

The repeater communications apparatus may further comprise an outputport configured to couple the delayed communications signal to radiofrequency transmission apparatus. The output port may be configured tocouple an optical signal to the radio frequency transmission apparatuswhere it is converted to a radio signal or may communicate a radiofrequency signal to the radio communications apparatus.

Typically, the repeater communications apparatus is further configuredto receive control signals for setting a length of the delay period.Thus, the apparatus may be user programmed in accordance with the delaynecessary for a particular cable network/system arrangement. Suitably,the communications apparatus further comprises a user interfaceoperative to receive user input and generate the control signalsresponsive to the user input.

The repeater communications apparatus may be further configured toprovide remote access to a user for receiving the control signals. Suchremote access allows a user to configure the delay in an apparatuswithout having to visit the location of the apparatus. This may beparticularly advantageous if new repeater communications apparatus isbeing added to an existing network necessitating reconfiguration of thedelays in existing repeater communications apparatus.

Typically, the length of the delay period is based upon the differencebetween a delay due to transmission of the signal over the cable from acommunications signal source to the repeater communications apparatusand the delay parameter.

In an embodiment the communications apparatus further comprisescommunications signal delay path apparatus which is user configurable todetermine the delay period.

The repeater communications apparatus may further comprise a transmitterstation arranged to transmit the delayed communications signal over theradio communications channel. The transmitter station may be integrallyformed with or housed with the communications apparatus therebyproviding a unitary repeater module.

Typically, the transmitter station is included as a part of atransceiver station thereby providing both downlink and uplinkcommunications.

In an embodiment of the communications system a first cable distancebetween the first repeater communications apparatus and the distributionmodule is greater than a second cable distance between the secondrepeater communications apparatus and the distribution module such thatthere is a difference between a first time taken for the communicationssignal to travel between the distribution module and the firstcommunications apparatus and a second time taken for the communicationssignal to travel between the distribution module and the secondcommunications apparatus. In such a system, the first communicationsapparatus is configured to introduce a first delay in the communicationssignal relative to the delay parameter and the second communicationsapparatus is configured to introduce a second delay in thecommunications signal relative to the delay parameter such that thedelayed communications signal at the first and second communicationsapparatus are synchronized to within a delay spread parameter for thesystem. The delay spread parameter defines the maximum delay betweenreceived signals that a mobile terminal can experience withoutexperiencing unacceptable levels of inter-symbol interference.

The delay parameter is at least as long as the first time taken for thecommunications signal to travel between the distribution module and thefirst communications apparatus. Generally, it may be made longer toprovide for timing tolerances and allow minor deviations in timing.

For a TETRA system utilizing Class A mobile terminals, the delay spreadparameter is about 15 μs. However, the delay spread parameter may begreater or lesser than 15 μs depending on the tolerance of thecommunications signal protocol to inter-symbol interference.

The cable network may comprise a ring topology and/or a directconnection (star) topology.

The features and advantages described in the specification are not allinclusive and, in particular, many additional features and advantageswill be apparent to one of ordinary skill in the art in view of thedrawings, specification, and claims. Moreover, it should be noted thatthe language used in the specification has been principally selected forreadability and instructional purposes, and may not have been selectedto delineate or circumscribe the disclosed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

The disclosed embodiments have other advantages and features which willbe more readily apparent from the detailed description, the appendedclaims, and the accompanying figures (or drawings). A brief introductionof the figures is below.

One or more embodiments in accordance with aspects disclosed herein willnow be described, by way of example only, with reference to theaccompanying drawings:

FIG. 1 is a schematic illustration of an embodiment disclosed herein;

FIG. 2 is a graphical representation of the time delay that may becaused by a signal travelling over a length of cable; and

FIG. 3 is schematic illustration of a second embodiment in accordancewith embodiments as disclosed herein.

DETAILED DESCRIPTION

The Figures (FIGS.) and the following description relate to preferredembodiments by way of illustration only. It should be noted that fromthe following discussion, alternative embodiments of the structures andmethods disclosed herein will be readily recognized as viablealternatives that may be employed without departing from the principlesof what is claimed.

Reference will now be made in detail to several embodiments, examples ofwhich are illustrated in the accompanying figures. It is noted thatwherever practicable similar or like reference numbers may be used inthe figures and may indicate similar or like functionality. The figuresdepict embodiments of the disclosed system (or method) for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles described herein.

FIG. 1 schematically illustrates an example embodiment 100 comprising abase transceiver station 102 coupled to an optical fiber distributionmodule 104 which feeds into optical fiber distribution network 105having a ring topology at network node 128. The optical fiberdistribution network 105 couples together a group of repeater antennas108, 112, 116 and 120, for propagating radio frequency (RF) signalscorresponding to the signals sent over the optical fiber distributionnetwork 105. A base transceiver station 102 transmits RF signals in afrequency band F1. As will be well-known to persons or the skilled inthe art, a frequency band comprises a number of individual carrierfrequencies each providing a respective communications channel.

The antennas 108, 112, 116 and 120 are distributed throughout an area inwhich radio propagation is difficult and interrupted, for example ahigh-rise urban environment, an in-building environment or anunderground environment such as a railway tunnel (for example, theLondon “Tube” system) or other underground facility. Each antenna 108,112, and 116 and 120 is respectively associated with a fiber enhancerunit 106, 110, 114 and 118. Each fiber enhancement unit 106, 110, 114and 118 is coupled to distribution network 105 at respective networknodes 150, 144, 138 and 132.

Each of the fiber enhancer and antenna pair is configured to take asignal from network 105 and up convert it to a RF signal in frequencyband F1. Although each antenna is disposed in an environment in whichradio propagation is difficult and interrupted RF signals transmittedfrom each antenna and also the base transceiver station 102 antenna maynevertheless interfere at a mobile terminal 160 thereby causinginter-symbol interference due to the delay between respective signalscaused by the different length of cable a signal has travelled overbefore being transmitted from a respective antenna as well as thedifference in distance between the mobile terminal 160 and respectiveantennas.

Turning now to base transceiver station 102 and optical fiberdistribution module 104, in general principle the base transceiverstation is coupled by an RF coupler to the optical fiber distributionmodule. An RF signal to be transmitted from base transceiver station 102is coupled to the optical fiber distribution module 104. In the opticalfiber distribution module 104 the RF signal is down converted to anoptical signal and output over cable 126 to network node 128. An exampleof an optical fiber distribution module is the “Optical Master Unit”provided by Axell Wireless Ltd of Asheridge Road, Chesham, Bucks, UK andset out in datasheet OMU_revB_web.

In the described embodiment the optical signal output from optical fiberdistribution module 104 exits network node 128 into network segment 130to begin a clockwise propagation through network 105. At each node 132,138, 144 and 150 the optical signal is tapped off to a respective fiberenhancer 118, 114, 110 and 106. Each fiber enhancer receives the opticalsignal and converts it to an RF signal in frequency band F1 and outputsthe RF signal to their respective antenna 120, 116, 112 and 108. Eachfiber enhancer unit may comprise any further repeater unit such asprovided by Axell Wireless Ltd with the details as set out in datasheetCSF Fiber fed repeater WCDMA_rev C_web for a WCDMA implementationoptionally an Optical Master Unit such as provided by Axell WirelessLtd. for receiving and optical signal and converting it to an RF signaloutput to a respective antenna.

At or associated with each fiber enhancer is a delay module, 119, 115,110 and 107 which in the embodiment illustrated in FIG. 1 operates on aninput optical signal. The delay module may be integrated with the fiberenhancer, for example it may be a software module which configures thedigital signal processing circuitry of a fiber enhancer to introduce thedelay. Optionally, the delay lines may be implemented as physical delaylines such as loops of cable.

The delay module will typically include a user interface for configuringa delay. The user interface may be remotely accessible so that it may beconfigured from a central location.

In the described embodiment, the network is a TETRA network as anexample of a communications system which may utilize the invention.Mobile terminal 160 may be a TETRA Class A terminal which typically cantolerate inter-symbol interference caused by up to around 15 μs of delayspread between received signals. Delay between received signals ofgreater than around 15 μs may generate sufficient inter-symbolinterference at mobile terminal 160 to cause it to be inoperable. Thevarious antennas 120, 116, 112 and 106 may be disposed such thatterminal 160 will not see a delay spread of greater than about 15 μsmerely due to the distance signals transmitted from each antenna have totravel to get to mobile terminal 160. However, the optical signal willtake an increasingly longer path to get antenna depending on where it isin the network ring topology.

In the described embodiment, the optical signal will travel acrosssegment 130 to node 132 and then over cable 134 to fiber enhancer 118where it is converted to an RF signal and transmitted from antenna 120.The signal transmitted from antenna 116 must also travel over segment136 to node 138 and then over cable 140 to fiber enhancer 114. Theoptical signal has to travel yet further over segment 142 to node 144and then over cable 146 to fiber enhancer 110 before being convertedinto an RF signal and transmitted from antenna 112. Yet further, theoptical signal travels over segment 148 to node 150 and then over cable133 to fiber enhancer 106 before being converted into an RF signal andtransmitted from antenna 108.

Typically propagation delay of an optical signal through optical fiberis about 5.48 μs per km for an average delay. The average propagationdelay for illustrative distances of optical fiber is set out as follows:

-   5 km has 27.4 μs average delay;-   10 km has 54.8 μs average delay;-   15 km has 82.2 μs average delay; and-   20 km has 109.6 μs average delay.

FIG. 2 is a schematic illustration of the above example distancessuperimposed on the ring network 105 illustrated in FIG. 1. Site Acorresponds to fiber enhancer 118 and antenna 120, site B corresponds tofiber enhancer 114 and antenna 116, site C corresponds to fiber enhancer110 and antenna 112, and site D corresponds to fiber enhancer 106 andantenna 108. In order to avoid inter-symbol interference experienced bymobile terminal 160 being due to two or more signals being received atgreater than a 15 μs delay spread, the fiber enhancer sites 118, 114,110 and 106 may have output synchronized. This may be synchronized to avalue at least greater than the greatest delay experienced at a fiberenhancer site due to fiber propagation delay, i.e., that experienced atfiber enhancer 106 (site D) in the illustrated embodiment.

In the illustrated embodiment the user definable value to which each ofthe sites may be synchronized is 137 μs which is the equivalent of theaverage propagation delay of an optical signal over a 25 km cable. Usingthe 137 μs delay in the embodiment illustrated in FIG. 1 having the ringtopology distances illustrated in FIG. 2 the following delays may beinserted at respective sites:

-   site A (5 km) is a distance 27.4 μs from the distribution module    node 128 and therefore fiber enhancer 118 will need to generate a    delay of 109.6 μs;-   site B (10 km) is a distance 54.8 μs from the distribution module    node 128 and therefore fiber enhancer 114 will need to generate a    delay of 82.2 μs;-   site C (15 km) is a distance 82.2 μs from the distribution module    node 128 and therefore fiber enhancer 110 will need to generate a    delay of 109.6 μs; and-   site D (20 km) is a distance 109.6 μs from the distribution module    node 128 and therefore fiber enhancer 106 will need to generate a    delay of 109.6 μs.

Respective delay modules are configured to have the delay correspondingto the site with which the delay module is associated as set out above.By introducing respective delays as set out above, the RF signalconverted from the output signal received at respective fiber enhancersand output from respective antennas is in synchronization. Therefore,mobile terminal 160 will only experience delay spread between two ormore signals due to the distance RF signals have to travel fromrespective transmitting antennas to the mobile terminal 160. Network 105can be arranged so that such delay spread will not exceed the 15 μsbeyond which inter-symbol interference causes the mobile terminal 160 tobe inoperative.

An optional network topology is illustrated in FIG. 3. The networktopology illustrated in FIG. 3 is a direct line (sometimes called a“star”) topology and each fiber enhancer 206, 210, 214 and 218 has adirect cable connection 252, 250, 254 and 256, to respective fiberenhancers. As with the embodiment illustrated in FIG. 1, each fiberenhancer is associated with a delay module configured to apply a delayto the optical signal received at the fiber enhancer. As before, it isimmaterial whether the delay is applied to the optical signal, the RFsignal output to respective antenna or an intermediate signal duringsignal processing conversion.

The direct cable connections to each of the enhancers are of differentlengths and for simplicity and ease of explanation the distance iscorresponds to be distances of each statement in the ring topology ofFIG. 1, namely 5 km, 10 km, 15 km and 20 km respectively. As for theembodiment of FIG. 1, a user definable value may be set to which each ofthe sites are synchronized which again can be 137 μs. The delay in eachfiber enhancer may be set to be: 109 μs for fiber enhancer 218; 82.2 μsfor fiber enhancer 214; 54.8 μs for fiber enhancer 210; and 27.4 μsfiber enhancer 206. In this way, the RF output from respective antennasare synchronized and any delay spread experienced by mobile turn a 160will we do to the difference in path taken by respective RF signals.

In each of the embodiments illustrated in FIG. 1 and FIG. 2 thepropagation delay in each fiber enhancer may be determined by completinga “ping” test. As will be known to persons of ordinary skill in the arta ping test is carried out by polling a device and waiting for aresponse, i.e., a message is sent to the unit and a response waited for.The total time includes the time the poll signal takes to reach thedevice and also the response sent back to the originator of the ping.Therefore, the time to the device is the total time minus the time togenerate a response at the device all divided by two.

In view of the foregoing description it will be evident to a personskilled in the art that various modifications may be made within thescope of the invention. For example, although the delay modules areillustrated as being integral with the fiber enhancers they may bephysically separate modules. Additionally, they may be remotelycontrollable from a central control station.

Although embodiments in accordance with the present invention have beendescribed with reference to the downlink direction of communication,similar issues arising in the uplink direction and may be solved usingthe same approach as described herein. Furthermore, the term basetransceiver station and acronym BTS are not intended to restrictembodiments in accordance with the invention to systems, standards orprotocols using such terminology but are generally intended to refer tocommunications equipment serving a geographic area with radiocommunications coverage providing downlink and/or uplink communications.

The user definable delay value to which respective fiber enhancers aresynchronized may be any suitable value and is not limited to theparticular values used in the illustrative embodiments.

Although the embodiment illustrated in FIGS. 1 and 3 show delay modulesacting on an optical signal, the delay may be introduced after theoptical signal has been converted to an RF signal or in the signalprocessing during conversion of the optical signal to an RF signal.Whether or not the delay is introduced into the optical signal, the RFsignal or some intermediate signal is not important for the purposes ofintroducing a delay. The delay could be introduced anywhere at therelevant fiber enhancer site.

Additionally, the delayed signal need not be transmitted at the samefrequency as the signal transmitted by the BTS 102, although it ispreferable to do so as such an arrangement provides for substantiallycontinuous coverage as a mobile terminal moves from the coverage area ofBTS 102 into the area served by the cable network and repeaterapparatus. That is to say, the coverage area of the BTS 102 iseffectively extended into the coverage area of the repeater apparatusformed by the fiber enhancer/antenna combinations since they transmit onthe same frequency.

Insofar as embodiments of the invention described above areimplementable, at least in part, using a software-controlledprogrammable processing device such as a general purpose processor orspecial-purposes processor, digital signal processor, microprocessor, orother processing device, data processing apparatus or computer system itwill be appreciated that a computer program for configuring aprogrammable device, apparatus or system to implement the foregoingdescribed methods, apparatus and system is envisaged as an aspect of thepresent invention. The computer program may be embodied as any suitabletype of code, such as source code, object code, compiled code,interpreted code, executable code, static code, dynamic code, and thelike. The instructions may be implemented using any suitable high-level,low-level, object-oriented, visual, compiled and/or interpretedprogramming language, such as C, C++, Java, BASIC, Perl, Matlab, Pascal,Visual BASIC, JAVA, ActiveX, assembly language, machine code, and soforth. A skilled person would readily understand that term “computer” inits most general sense encompasses programmable devices such as referredto above, and data processing apparatus and computer systems.

Suitably, the computer program is stored on a carrier medium in machinereadable form, for example the carrier medium may comprise memory,removable or non-removable media, erasable or non-erasable media,writeable or re-writeable media, digital or analog media, hard disk,floppy disk, Compact Disk Read Only Memory (CD-ROM), Compact DiskRecordable (CD-R), Compact Disk Rewriteable (CD-RW), optical disk,magnetic media, magneto-optical media, removable memory cards or disks,various types of Digital Versatile Disk (DVD), subscriber module, tape,cassette, solid-state memory. The computer program may be supplied froma remote source embodied in the communications medium such as anelectronic signal, radio frequency carrier wave or optical carrierwaves. Such carrier media are also envisaged as aspects of the presentinvention.

As used herein any reference to “one embodiment” or “an embodiment”means that a particular element, feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

In addition, use of the “a” or “an” are employed to describe elementsand components of the invention. This is done merely for convenience andto give a general sense of the invention. This description should beread to include one or at least one and the singular also includes theplural unless it is obvious that it is meant otherwise.

The scope of the present disclosure includes any novel feature orcombination of features disclosed therein either explicitly orimplicitly or any generalization thereof irrespective of whether or notit relates to the claimed invention or mitigate against any or all ofthe problems addressed by the present invention. The applicant herebygives notice that new claims may be formulated to such features duringprosecution of this application or of any such further applicationderived therefrom. In particular, with reference to the appended claims,features from dependent claims may be combined with those of theindependent claims and features from respective independent claims maybe combined in any appropriate manner and not merely in specificcombinations enumerated in the claims.

1. Communications signal repeater apparatus, configured to: receive acommunications signal from a cable; delay said communications signal bya delay period relative to a delay parameter; and configure a delayedcommunications signal for transmission over a radio communicationschannel.
 2. The communications apparatus according to claim 1, furthercomprising an output port configured to couple said delayedcommunications signal to radio frequency transmission apparatus.
 3. Thecommunications apparatus according to claim 1, further configured toreceive control signals for setting a length of said delay period. 4.The communications apparatus according to claim 3, further comprising auser interface operative to receive user input and generate said controlsignals responsive to said user input.
 5. The communications apparatusaccording to claim 3, further configured to provide remote access to auser for receiving said control signals.
 6. Communications apparatusaccording to claim 1, further configured to set said length of saiddelay period based upon the difference between a delay due totransmission of said signal over said cable from a communications signalsource to said communications apparatus and said delay parameter.
 7. Thecommunications apparatus according to claim 1, further comprisingcommunications signal delay path apparatus user configurable todetermine said delay period.
 8. The communications apparatus accordingto claim 1, further comprising a transmitter station arranged totransmit said delayed communications signal over said radiocommunications channel.
 9. The communications apparatus according toclaim 8, further comprising a transceiver station incorporating saidtransmitter station.
 10. The communications apparatus according to claim1, wherein said cable comprises an optical cable.
 11. A communicationssystem, comprising: a cable network for distributing a communicationssignal; a communications signal distribution module operative to receivea communications signal for distribution over said cable network andconfigurable to couple to said cable network; and first and secondcommunications apparatus according to any preceding claim respectivelycoupled to said cable network for receiving said communications signalfrom said distribution module.
 12. The communications system accordingto claim 11, wherein a first cable distance between said firstcommunications apparatus and said distribution module is greater than asecond cable distance between said second communications apparatus andsaid distribution module such that there is a difference between a firsttime taken for said communications signal to travel between saiddistribution module and said first communications apparatus and a secondtime taken for said communications signal to travel between saiddistribution module and said second communications apparatus.
 13. Thecommunications system according to claim 12, wherein said firstcommunications apparatus is configured to introduce a first delay insaid communications signal relative to said delay parameter and saidsecond communications apparatus is configured to introduce a seconddelay in said communications signal relative to said delay parametersuch that said delayed communications signal at said first and secondcommunications apparatus are synchronized to within a delay spreadparameter for said communications system.
 14. The communications systemaccording to claim 13, wherein said delay parameter is at least as longas said first time taken for said communications signal to travelbetween said distribution module and said first communicationsapparatus.
 15. The communications system according to claim 13, whereinsaid delay spread parameter is 15 μs.
 16. The communications systemaccording to claim 11, wherein said cable network comprises one of aring topology or a direct connection topology.
 17. The communicationssystem according to claim 11, wherein said cable network comprises anoptical cable network.
 18. A method of synchronizing signals transmittedfrom two or more communications apparatus coupled to receive acommunications signal distributed over a cable network, the methodcomprising: introducing a first delay in said communications signalrelative to a delay parameter in a first communications apparatus;introducing a second delay in said communications signal relative tosaid delay parameter in a second communications apparatus; wherein saidfirst and second delay are configured to delay said communicationssignal at said first and second communications apparatus such that theyare synchronized to within a delay spread parameter for said cablenetwork.
 19. A method according to claim 18, wherein said delay spreadparameter is 15 μs.
 20. The method according to claim 18, wherein saiddelay parameter is at least as long as the time taken for saidcommunications signal to travel to the furthest one of said first andsecond communications apparatus.
 21. The method according to claim 19,wherein said delay parameter is at least as long as the time taken forsaid communications signal to travel to the furthest one of said firstand second communications apparatus.
 22. The method according to claim18, wherein said cable network is an optical cable network.